1. Field of the Invention
This invention relates to vehicular semi-automatic mechanical transmission systems and, in particular, to semi-automatic mechanical transmission systems of the type providing partially automatic implementation, including an automatic shift into neutral upon a driveline torque break or torque reversal condition, of preselected shifts and having at least one automatic preselect mode of operation wherein ratio changes are automatically preselected by the system central processing unit.
More particularly, the present invention relates to semi-automatic transmission systems of the type described above wherein, in the operator selected automatic preselection mode of operation, if vehicle speed (output shaft speed) remains substantially constant (i.e. if, for upshift conditions, output shaft acceleration does not exceed a first reference value, or, for downshift conditions, output shaft deceleration does not exceed a second reference value) then automatic preselection of shifts and automatic shifts into sustained neutral are prevented to prevent unexpected/undesired transmission shifts into sustained transmission neutral.
Still more particularly, the present invention relates to semi-automatic transmission systems of the type described above wherein, if engine or input shaft speeds are between certain values, the values of the first and second reference values will vary as a function of engine or input shaft speed.
2. Description of the Prior Art
Fully automatic transmission systems, both for heavy-duty vehicles such as heavy-duty trucks, and for automobiles, that sense throttle openings or positions, vehicle speeds, engine speeds, and the like, and automatically shift the vehicle transmission in accordance therewith, are well known in the prior art. Such fully automatic change gear transmission systems include automated transmissions wherein pressurized fluid is utilized to frictionally engage one or more members to other members or to a ground to achieve a selected gear ratio as well as automated mechanical transmissions utilizing electronic, hydraulic, and/or pneumatic logic and actuators to engage and disengage mechanical (i.e. positive) clutches to achieve a desired gear ratio. Examples of such transmissions may be seen by reference to U.S. Pat. Nos. 3,961,546; 4,081,065; 4,361,060 and 4,551,802; the disclosures of which are hereby incorporated by reference.
Such fully automatic change gear transmissions can be unacceptably expensive, particularly for the largest heavy-duty vehicles which are not typically sold in high volumes. Additionally, those automatic change gear transmissions utilizing pressurized fluid and/or torque converters tend to be relatively inefficient in terms of power dissipated between the input and output shafts thereof.
Semi-automatic transmission systems utilizing electronic control units which sense throttle position, engine, input shaft, output shaft and/or vehicle speed, and utilize automatically controlled fuel throttle devices, gear shifting devices and/or master clutch operating devices to substantially fully automatically implement operator manually selected transmission ratio changes are known in the prior. Examples of such semi-automatic transmission systems may be seen by reference to U.S. Pat. Nos. 4,425,620; 4,631,679 and 4,648,290, the disclosures of which are incorporated herein by reference.
While such semi-automatic mechanical transmission systems are very well received as they are somewhat less expensive than fully automatic transmission systems, allow manual clutch control for low speed operation and/or do not require automatic selection of the operating gear ratio, they may be too expensive for certain applications as a relatively large number of sensors and automatically controllable actuators, such as a master clutch and/or a fuel throttle device actuator, are required to be provided, installed and maintained.
Many of the drawbacks of the prior art are overcome or minimized by the previous provision of a semi-automatic shift implementation system/method for a mechanical transmission system for use in vehicles having a manually or partially automatically controlled engine throttle means, and a manually only controlled master clutch. The system has, preferably, a manual preselection mode wherein shifts are manually preselected and at least one mode of operation wherein the shifts to be semi-automatically implemented are automatically preselected and includes a control/display panel or console for operator selection of operation in the automatic preselection mode and indication of automatic preselection of upshifts, downshifts or shifts into neutral. An electronic control unit (ECU) is provided for receiving input signals indicative of transmission input and output shaft speeds and for processing same in accordance with predetermined logic rules to determine, in the automatic preselection mode, if an upshift or downshift from the currently engaged ratio is required and to issue command output signals to a transmission actuator for shifting the transmission in accordance with the command output signals.
The control/display device will display the selected but not yet implemented shift as well as the current status of the transmission, and, preferably will allow the operator to select/preselect a shift into a higher ratio, a lower ratio or into neutral. Preferably, the control device will also allow a manually or an automatically preselected shift to be cancelled.
In both the manual and the automatic preselection modes, when a ratio change is manually or automatically preselected, the transmission will automatically be urged or biased to shift, upon a driveline torque break or reversal, to neutral and will then shift to the selected ratio only upon the operator manually causing a substantially synchronous condition to exist.
In accordance with the previously proposed control, a control system/method for a vehicular semi-automatic mechanical transmission system for partially automatic implementation of manually and automatically preselected transmission shifts was provided which did not require throttle or clutch actuators, and which required only two speed signal inputs. However, this system was not totally satisfactory as, after a long period of relatively stable vehicle operating conditions, i.e. vehicle speed substantially constant or changing at less than a predetermined rate, an automatic preselection of automatic shifting of the transmission into, and remaining in, neutral may be undesired, unexpected and/or startling to the operator. This can occur during unintended torque breaks caused by cresting a hill, bumps in the road, and similar occurences.